A blast had been heard near the finish line before the race ended, but a security official said it was a controlled explosion

Receive the latest national-international updates in your inbox

Greg Van Avermaet of Belgium celebrates after crossing the finish line to win the men's cycling road race final followed by Jakob Fuglsang of Denmark at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Saturday, Aug. 6, 2016.

At the end of a six-hour, 10-minute ride, Belgian cyclist Greg Van Avermaet chased down a breakaway rider and burst to victory at the men's cycling road race.

The road race has been described as a grueling showcase for everything from the sun-splashed beaches of Copacabana and Ipanema to the squalor of the nearby slums.

Van Avermaet and Denmark's Jakob Fugsang worked together to reel in Rafal Majka, of Poland, who led the field in the race until the last kilometer. With a big kick, the Belgian pulled ahead and crossed the finish line all alone.

Attention had shifted to the finish line with about 70 kilometers to go was when a small blast shook the area. No one was injured, and the 6-hour event went on unaffected. Reporters heard a loud boom on the press tribune and felt the ground shake. An officer assigned to the event said it was a controlled explosion of an unattended bag.

The race unfolded against a backdrop of historic Fort Copacabana and the long, fast flats along the brilliant blue waters of the Atlantic. There are the harrowing climbs and brutal descents on slick roads twisting through jungle, and the jarring cobblestone sections that add a little spice and a lot of bumps.

"It's the hardest course I've seen in a single-day race," said American rider Megan Guarnier, who made a special trip to Brazil just to scout the course. "It has everything in it."

Which is precisely the point. The road race has always been a showpiece of cycling, positioned first in the program and rolling off the morning after the opening ceremony.

The race at the Beijing Olympics in 2008 sent riders past the iconic Temple of Heaven, Tiananmen Square and portions of the Great Wall of China. Like the course in Rio, it then sent riders off into the countryside, though the elevation changes were nothing like they will face in Brazil.

Four years ago, the London Olympics course started and ended with the spectacular setting of Buckingham Palace. More than a million people lined the route, packing the climb of Box Hill in the green Surrey countryside, in a nod to cycling fever that gripped the country in the days after Bradley Wiggins won Britain its first Tour de France.

"I'm surprised someone signed off on a course this hard," New Zealand's George Bennett said. "It's hectic, it's dangerous. There are slippery roads, patches of oil, difficult corners. It could send you home early. But it's the kind of racing I like. I like the chaos."

The chaos began when the men rolled off from the century-old fort Saturday morning. They covered 236 kilometers (146 miles), more than any single stage of the Tour, and climbed 3,600 meters (11,800 feet), on par with hard one-day races such as Liege-Bastogne-Liege.